1. Field of the Invention
The present invention relates to an enhanced optical transceiver arrangement, and in particular, to an enhanced optical transceiver arrangement that can be optically coupled with an optical fiber ribbon for receiving and transmitting optical signals thereto and therefrom.
2. Background Information
Computer and communication systems are now being developed in which optical devices, such as optical fibers, are used as a conduit (also known as a wave guide) for modulated light waves to transmit information. These systems typically include a light emitter or a light detector optically connected to the optical fibers. A typical light emitter may be a so-called edge emitter, or a surface emitter, such as a vertical cavity surface emitting laser (VCSEL). A typical light detector may be a photodiode. A generic term of either a light emitter or a light detector is an xe2x80x9coptoelectronic transducer.xe2x80x9d A generic term for a light emitter and a light detector arrangement is an optical transceiver. The optical fibers, which collectively form a fiber-optic cable or ribbon, are typically coupled to the respective light detector and the light emitter, so that optical signals can be transmitted back and forth, for example.
As an example, optoelectronic transducers convert electrical signals to or from optical signals; the optical signals carry data to a receiver (light detector) from a transmitter (light emitter) at very high speeds. Typically, the optical signals are converted into, or converted from, the associated electrical signals using known circuitry. Such optoelectronic transducers are often used in devices, such as computers, in which data must be transmitted at high rates of speed.
The conventional light emitter allows for integrated two-dimensional array configurations. For example, the active regions of a conventional VCSEL can be arranged in a linear array, for instance 12 active regions spaced about 250 microns apart, or in area arrays, for example, 16xc3x9716 arrays or 8xc3x978 arrays. Of course, other arrangements of the arrays are also possible. Nevertheless, linear arrays are typically considered to be preferable for use with optoelectronic transducers, since it is generally considered easier to align the optical fibers that collect the light emitted from the VCSELs in a linear array, than in an area array. Moreover, it is also possible to utilize the active regions singly, i.e., without being arranged in an array.
The optoelectronic transducers are normally located on either input/output cards or port cards that are connected to an input/output card. Moreover, in a computer system, for example, the input/output card (with the optoelectronic transducer attached thereto) is typically connected to a circuit board, for example a mother board. The assembly may then be positioned within a chassis, which is a frame fixed within a computer housing. The chassis serves to hold the assembly within the computer housing.
Typically, each optical fiber of the ribbon is associated with a respective active region. Further, it is conventional for the ends of the optical fibers of the ribbon to terminate in a fiber connector. Such fiber connectors usually have an industry standard configuration, such as the MTP(copyright) fiber connectors manufactured by US Conec, Ltd. of Hickory, N.C. However, fiber connectors having the industry standard configuration are not suitable for connecting directly with the sensitive active regions of the typical light emitters or light detectors. Should direct contact occur between the respective active regions and the fiber connector, the fiber connector would likely damage the active regions, causing the light emitter or light detector to become inoperative. It is thus conventional to space the fiber connector away from the active regions. However, as will be appreciated, by providing a space, it thus becomes desirable to provide a way of optically coupling the active regions with the fiber connector, so that the optical signals can be accurately and efficiently transmitted therebetween.
One conventional manner of optically coupling the active regions with the fiber connector is to provide a lens assembly in the space therebetween. However, lens assemblies tend to be complicated and expensive. Thus, it is also known to provide a fiber optic coupler between the active regions and the fiber connector. However, the conventional fiber optic coupler has a limited length, due to manufacturing constraints. Thus, the known fiber connectors must be positioned relatively close to the active regions, which may limit design options.
Moreover, the typical optical transceiver arrangement utilizes separate modules for both the light emitter and light detector, thus requiring a substantial amount of board space. Further, such separate modules are often difficult to assemble in the tight confines provided. Thus, it is desirable to provide an optical transceiver arrangement that does not occupy much space. Moreover, it is further desirable to provide an optical transceiver arrangement that is relatively easy to assemble and place in its desired location. Additionally, it is desirable to provide an optical transceiver arrangement in which the light emitter and the light detector are provided in the same package.
It is, therefore, a principal object of this invention to provide an enhanced optical transceiver arrangement.
It is another object of the invention to provide an enhanced optical transceiver arrangement that solves the above mentioned problems.
These and other objects of the present invention are accomplished by the enhanced optical transceiver arrangement disclosed herein.
According to one aspect of the invention, the optical transceiver arrangement is formed from a plurality of interconnected subassemblies. One of the subassemblies is a retainer assembly, which includes a retainer and a carrier assembly. The carrier assembly includes a die carrier, having opposing lands. The opposing lands have a receiving space therebetween, in which either a light emitter die chip or light detector die chip (hereinafter referred to collectively as a die chip) is disposed.
The carrier is preferably manufactured from a conductive material, so that it can serve as a ground for the die chip. For example, the carrier can be formed from copper, and be gold plated to enhance its conductivity and reduce its susceptibility to oxidation.
The carrier further has spaced apart feet, which can be attached to a further subassembly of the optical transceiver arrangement, as will be subsequently described. The feet provide a space under the carrier in which other components can be disposed.
Each land is adapted to allow an optical coupler to be attached thereto. The optical coupler is adapted to optically couple active regions of the light emitter or light detector with a fiber connector (i.e., an industry standard connector attached to an end of an optical fiber ribbon), so that optical signals can be accurately transmitted therebetween. For example, each land can be provided with a receiving hole, which receives a corresponding alignment pin of the optical coupler in a clearance type fit.
The optical coupler includes at least two plates disposed in a superposed relationship. At least one of the plates, or alternatively both of the plates, has a plurality of spaced apart narrow grooves formed in a surface thereof, each of which extends from one end face to another end face of the plates. Each of the narrow grooves has an optical fiber disposed therein, i.e., a fiber that is separate and distinct from the optical fibers of the ribbon. Further, the plate or plates may have a plurality of wide grooves formed in the surface. Each wide groove extends from a respective end face toward an intermediate portion of the plate or plates, for example. Each of the wide grooves has an alignment pin disposed therein. When the plates are joined together in the superposed relationship, the narrow grooves form through holes for the respective optical fibers, and the wide grooves form wide holes for the alignment pins. When formed, each of the optical fibers of the optical coupler are alignable with respective ones of the active regions of the die chip, respective ones of the alignment pins are insertable into the receiving holes in the lands of the carrier, and respective other ones of the alignment pins are engagable with the fiber connector.
The optical fibers of the optical coupler may be actively aligned with the active regions, so as to ensure that the emitted light does not partially or completely xe2x80x9cmissxe2x80x9d its intended target. Thereafter, a UV curable adhesive, for example, could be used to fix the respective alignment pins in the respective receiving holes in the lands, thereby locking the optical coupler in alignment with the active regions of the die chip.
After alignment, an epoxy, for example, can be used to seal the exterior edges of the optical coupler to the surface of the die chip. The epoxy may have a sufficiently high viscosity so as to prevent the epoxy from flowing into the gap between the edge of the optical coupler and the active regions of the die chip. Thus, a sealed air gap will be formed between the ends of the optical fibers in the coupler and the active regions to allow for the transmission of light, while preventing contaminants from entering this space.
The carrier assembly further includes a flex cable that is electrically coupled to the die chip. The flex cable has both ground wires (or a ground layer) and signal wires which may be covered by an insulating coating, such as plastic. The insulating coating may be removed in a region at one end of the flex cable, to form one or more xe2x80x9cwindowsxe2x80x9d which expose the signal wires, grounds wires or both as they pass through the space of the windows. For example, if the flex cable is provided with two windows, one disposed over the other, the lower window can be adapted to expose the ground wires, to allow the ground wires to be electrically coupled to the conductive carrier. The upper window can then be adapted to expose the signal wires, which can then be electrically coupled to the die chip. This arrangement works well when the die chip is attached and directly grounded to the carrier. Alternatively, if the die chip is not directly grounded to the carrier, then the flex cable can be provided with only one window, which is adapted to expose both the ground wires and the signal wires. These can then be electrically coupled to the die chip, for example a light detector die chip, to provide both a signal path and a return ground path.
Another end of the flex cable may also be provided with a conductive plate, such as a metal stiffener, electrically bonded to the ground wires/ground layer of the flex cable. This conductive plate can then be attached to a ground potential, in a manner that will be subsequently described.
In use, the flex cable may be arranged to extend down the front of the carrier (i.e., on the side the die chip is disposed), and then flexed and bent to pass between the feet of the carrier and through the space therebetween. Thus, the conductive plate will then be disposed in a region behind the carrier.
The retainer assembly further includes the retainer, into which the carrier assembly is disposed. The retainer has a housing formed from an insulating material, such as a polymer, for example. The housing has a through hole extending therethrough. The carrier assembly is placed into a rear end of the through hole and arranged so that the coupler is disposed almost entirely within the through hole, with the carrier being disposed outside of the through hole. Once in position, the carrier assembly can be fixed to the housing, for example, by adhering the coupler to the walls defining the through hole. The adhering can be accomplished using a UV structural epoxy, or a thermal initiated epoxy, for example, which would provide the resulting structure with a desired rigidity.
The retainer may also be provided with latching fingers disposed at a front end of the through hole. The latching fingers are adapted to engage with an industry-standard fiber optic connector, which is plugable into the retainer via the front end of the through hole.
The housing and fingers are preferably molded to have a one-piece configuration. This reduces assembly time by eliminating the need to fix separate latching fingers to the housing, and reduces inventory by eliminating multiple parts.
In a further exemplary aspect of the invention, the front end of the retainer may also be provided with an electromagnetic interference shield. The electromagnetic interference shield is preferably formed from a conductive, non-corrosive material, such as steel having a tin plating. However, the electromagnetic interference shield can be formed of any material that will attenuate electromagnetic interference.
The electromagnetic interference shield is hollow, to allow the shield to be slipped over the front end of the retainer. When properly positioned, the edge of the electromagnetic interference shield will be positioned essentially flush with the front end of the retainer. The shield may be provided with inwardly projecting fingers that engage with the surface of the retainer, to hold the shield in place.
The electromagnetic interference shield may be provided with a number of conductive grounding springs, which are disposed around the outer periphery of an end of the shield. The grounding springs may engage with a tailstock, for example, to conductively couple the electromagnetic interference shield to a ground potential. When properly positioned, the grounding springs hold the electromagnetic interference shield in a fixed position relative to the tailstock.
The shield can be used to hold the first and second housings together, when two housings are provided. That is, the shield can be slid around the adjacent housings, and serve as a clamp to retain the housings in their relative positions.
The optical transceiver arrangement may further include a laminate assembly. The laminate assembly includes a printed circuit board or wiring board, that has a plurality of superposed, alternating conductive layers and insulating layers formed in discrete planes. A front surface of the wiring board may have various electronic components, such as a light emitter driver chip and/or light detector driver chip, attached thereto, and may have electrically conductive pathways or wirings (also known as traces) between the components. The driver chips may be positioned so that in the final optical transceiver arrangement, the driver chips are positioned away from the carrier to aid in heat dissipation.
The printed circuit board can be adapted to allow it to be attached to a further printed circuit board, for example, by an end user. By way of example, the lower surface of the printed circuit board can be provided with a plurality of conductive pads arranged in an array, each of which is coupled to a ground plane, power plane and wiring plane of the board, using vias, for example, and each of which may be attached to a respective lead of a further printed circuit board using ball grid array (BGA) technology.
The laminate assembly may further include a polymer coating disposed on the upper surface of the printed circuit board, and upon which the retainer assembly can be disposed. The polymer coating may be relatively thick, and formed to provide locating features to facilitate the positioning of the various other subassemblies. For example, the housing of the retainer assembly may be provided with one or more projecting pins on a lower surface thereof, and the polymer coating may be provided with receiving holes that accommodate the respective projecting pins. Thus, during manufacturing, the retainer assembly can be quickly located on the laminate assembly in the desired location. Moreover, the coating protects the wirings and components on the surface of the circuit board, and helps to distribute heat generated by the drivers over a larger surface area.
Moreover, the polymer coating may be provided with one or more recesses formed therein, to expose respective conductive pads that are electrically coupled to the ground plane. The feet of the carrier can then be electrically bonded, using an electrical epoxy for example, to the conductive pads so that the carrier is electrically coupled to the ground plane. Moreover, the conductive plate of the flex cable may be electrically bonded to another conductive pad, to provide another means of electrically coupling the ground plane to the die chip and carrier. Further, the signal wires of the flex cable may be coupled, for example wire bonded, to respective signal traces on the surface of the laminate. Thereafter, the various electrical connections can be coated to protect the connections and wires from being damaged. For example, the coating can be a so-called chip coat epoxy material.
During the coupling of the flex cable to the laminate assembly, the retainer assembly housing may also be fixed to the laminate assembly. For example, the housing or housings may be epoxied to the laminate assembly.
In another exemplary aspect of the invention, the optical transceiver arrangement may include a cover member including a heat sink disposed over the laminate assembly. In this exemplary aspect of the invention, the polymer coating may include a step arranged around an outer periphery thereof, and the heat sink cover may have a flange that engages with the step to position the heat sink cover relative to the laminate assembly. Once in position, the heat sink cover can transfer and dissipate heat generated by the drivers, for example.
The heat sink cover may also be provided with a downwardly-projecting finger that is adapted to engage with an exposed conductive pad of the printed circuit board, which is coupled with the ground plane. In this manner, when the heat sink cover is in position, the heat sink cover will be electrically coupled with a ground potential, allowing the heat sink cover to serve as a further ground potential for the light emitter/light detector. Moreover, the downwardly-projecting finger can be positioned to extend between the adjacent housings, and in particular between the respective light emitter and light detector when so provided, to serve as an electromagnetic emissions separator. Thus, the heat sink cover can help prevent electromagnetic interference from occurring between the light emitter and light detector.
When properly positioned, the heat sink cover may be bonded in place, for example using an epoxy, and may be positioned to abut against a back of the retainer assembly.